Metal plating by a wet mechanical process



May 13, 1969 J. E. CUTCLIFFE METAL PLATING BY A WET MECHANICAL PROCESS Filed April 2, 1964 INVENTOR .JO/I/V 5. CZ/TCL/FFE,

BY $01 w ATTOR NEYS United States US. Cl. 117109 12 Claims ABSTRACT OF THE DISCLOSURE A wet process for mechanically plating metal powder on metal articles wherein an impactor material consisting of hard bodies having entirely microscopically smooth non-metallic and non-ionizable outer surfaces resistant to metal coating in a liquid carrier, for example glass balls, is utilized in the presence of a liquid carrier to forcibly impact a coating of the metal powder onto the articles to be plated.

The present application is a continuation-in-part of my copending application Ser. No. 682,847, filed Sept. 9, 1957, and now abandoned.

This invention relates to a new mechanical metal plating process, and more particularly, to a Wet plating process using special impactors to promote plating.

As known in the art, mechanical metal plating generally consists in the utilization of particles of metal dust which are hammered, impacted or otherwise pressure applied to the surfaces of various articles, thereby forming a permanent metallic coating. Heretofore, the hammering or impacting has been effected by the use of impacting media such as round iron or steel shot, crushed shot, nailed clippings, cut iron pellets, Alundum chips, silicon carbide, sand, metal turnings, or nuts and bolts. Basically, an impacting medium is placed in a ball mill along with a charge of the metal dust or particles, and the articles to be coated. The ball mill is then tumbled sufliciently to produce a hammering of the particles onto the articles. The coating results from a build up of layers of mechanically bonded particles. Often, there is also included a substantial quantity of promoter substances in a liquid carrier, including film-forming materials and metal deoxidizers, to enhance and promote the plating process. This latter feature, known as wet plating, produces a substantially superior coating. Coating without liquids is known as dry plating.

Mechanical plating, as practised, is exemplified or defined in such patents as 2,640,001; Re. 23,861; 2,689,808 and 2,723,204 and copending applications Ser. No. 670,355, now abandoned in favor of Ser. No. 267,854 now U.S. Patent 3,132,043; Ser. No. 357,203, now US. Patent No. 3,023,127; and Ser. No. 388,702 filed Oct. 27, 1953 and now abandoned.

In practicing the known processes of mechanical metal plating, the use of any one of the above-listed metallic impacting media in a ball mill results in a very effective, bright and permanently adhered metallic coating on the articles. However, when utilizing, for example, steel balls as impactors during the coating, metal flakes are impacted onto and will coat the surfaces of the steel balls. Similar results occur when using any of the other known media as impactors. Moreover, an initial coating on the impactors promotes further impactor coating, resulting in the surface of the impactors becoming rough or irregular, and the proportion of the metal powder deposited on the articles substantially decerases as the coating on the impactors increases. Since the surface area of the impact- 3,443,985 Patented May 13, 1969 ing media is usually much greater than that of the articles, and the roughening of the media surfaces enhances their plateability, the deleterious effect of plating of the impactors becomes progressive. Consequently, commercial use often becomes impractical, because of the substantial weight loss of valuable metal particles. Of course, whenever, possible, the impactors are subjected to a process for removing the coating thereon. But even where possible, the removal operation requires a substatnial amount of time and expense.

An important object of the present invention, therefore, resides in the new use of certain impacting media to mechanically plate articles with a permanent metal coatmg.

Yet another object of the invention resides in the use of a new impacting medium in a particular mechanical plating process, which impacting medium possesses char acteristics preventing plating by the metal particles thereon during the plating process.

Still another object of the invention is in the use of a particular non-metallic, smooth surfaced, non-plateable impacting medium in a metal plating process utilizing liquid promoting substances or promoter substances in a liquid carrier.

A more particular object of the invention resides in the use of glass spheres, beads or other spheroidal-shaped glass surfaces as impacting media in the mechanical wet plating process.

By the process in accordance with the present invention, there is produced a bright metal-covered article having a coating generally characterized by numerous, generally spheroidal metallic particles permanently mechanically welded or bonded together and to the base article. Coating according to the present invention is substantially accelerated, because only the base articles are coated.

Other objects and advantages will become apparent from the following description, the accompanying drawing forming a part thereof and wherein:

FIGURE 1 is a schematic representation of a longitudinal, sectional view of a coating applied to a substrate in accordance with the present invention.

FIGURE 2 is a schematic representation of a longitudinal, sectional view of a coating applied to an article made with a wet plating process.

FIGURE 3 is a cross-sectional view of metal shot after use in a typical mechanical plating process.

FIGURE 4 is a cross-section of glass beads after use in a dry plating process; and

FIGURE 5 is a cross-section of glass beads used in accordance with the present invention.

Specifically referring to the coating on the substrate N in FIG. 1, it is significant to note that the microstructure thereof is distinctively different from prior coatings. The coating, genenally denoted at C, is at its inner surface S homogeneously mechanically welded and bonded to the surface of the substrate, and in superposed relation thereto there is a heterogeneous disposition of the metal particles P. These metal particles P are, in the main, spheroidal in outline and they are of various sizes. The particles P, being substantially spheroidal, are joined to each other at what are essentially points D rather than large areas of contact, and this is effected by the hammering of the glass spheroids or the like against the metal particles, which said particles are thereby impacted and compacted, as shown in the drawings, to the surface of the article that is to be coated. interspersed between the particles P are minute inclusions of the utilized filmformer F.

This coated structure illustrates another of the advantages obtained by use of the nonplateable impacting medium in that the speed with which plating is accomplished is much higher than with previously utilized impacting materials. The metal coating is impacted and built up at a highly accelerated rate so that there is not sufficient time for the individual metal powder particles to become appreciably elongated before they are integrated into the coating and, after the coating is built up, substantial elongation cannot take place due to astriction of any one particle within the coating.

In prior mechanical metal plating, especially where steel balls, shot or the like typical prior art impacting medium are utilized in the process of plating and as illustrated in FIGURE 2, the metal particles P have been impacted to such a degree as to be considerably elongated and flattened out and formed in sort of discrete layers or laminae, and which constituted a very eifective coating but one varying in characteristics quite differently from the coating as obtained by the use of the glass spheroids in the mechanical plating process of the present invention. It has been found with respect to the present invention that it is not necessary that the metal particles be elongated laterally and flattened to produce an effective coating or cladding of the metal about an object or objects. To the contrary, the coating as produced in the present invention, which in the main consists of the spheroidally shaped metal particles mechanically point contactingly engaged with each other in a heterogeneous manner, is a unique and distinctive coating having the characteristics of being of sufficient density as to etfectively presserve the article coated and the smoothness and brightness of the surface thereof as to present pleasing appearing articles coated in accordance with the invention, and yet said coating on the article being so firmly adhered thereon as to be quite difficult of accidental or unintentional removal therefrom.

The coatings shown in FIGURES 1 and 2 were both produced generally by using the wet plating process as described, for example, in copending applications Ser. No. 357,203, now U.S. Patent No. 3,023,127; and Ser. No. 267,854, now U.S. Patent 3,132,043, wherein the articles to be plated and the metal particles were placed in a ball mill containing a liquid carrier medium having a film-forming compound and an oxide solvent. However, the coating shown in FIGURE 1 was produced according to the present invention by including within the ball mill, an impacting medium comprising small spheres or substantially spherical and smooth-surfaced objects of a non-metallic material eifectively resistant to plating by metal, i.e., glass spheres. The coating shown in FIGURE 2 was obtained by using steel shot as the impacting medium, in accordance with the particular procedures as outlined in copending applications Ser. Nos. 357,203 and 267,854.

The marked difference between the two coated structures is clearly shown in FIGURES l and 2. For example, FIGURE 1 depicts the metal particles, while homogeneously mechanically welded to the surface of the base article and to each other, remain substantially in a spheroidal shape and are joined to each other by essentially point contact. Included between the particles are minute quantities of the film-forming material aiding in retaining the coating. Because coating accordance with the above process is highly accelerated, the particles do not become appreciably elongated during the build-up of the coating, and perhaps this is due to the lower density of the impacters utilized by the present invention.

As illustrated in FIGURE 2, the particles in the coating from a typical wet plating process are laterally elongated and flattened to obtain a major metal to metal contact, with smaller interspersed inclusions of the film-forming material.

FIGURES 3 to 5 illustrate the problem of particle de pletion, as solved by the present invention. FIGURE 3 shows typical iron shot ll after use as impactors in a wet plating operation and having a substantial metal coating 2 derived from the metallic powder particles used for coating. As will be noted, the coating surface is irregular, and because it is of the same metal as the particles, coating tends to build through a cohering interatomic bonding of like metal particles. The film-formers used to create a physically affinative molecularly thin film add to the cohesive attraction tending to build up a permanent coating 2 on the iron shot 1.

FIG. 4 shows impactor 3, plastic or glass, used in a dry plating process, described for example in U.S. Patent No. 2,723,204 and copending application Ser. No. 726,354, now U.S. Patent No. 3,093,501. Here the impactors 3, whether steel, plastic or glass, become coated with a thin layer 4 of the metallic powder; and this layer 4 also tends to build, although not as rapidly as layer 2.

By the present invention, the smooth surfaced glass beads 5 shown in FIG. 5 may be used continually in a wet plating process without any coating or build up on the impaetors. The impactors 5 remain clear, thereby enabling all of the metal powder to be used for coating of the articles.

At least one essential requirement of the impacting medium in accordance with the present invention is that it be fabricated from glass or have glass-like surfaces which are extremely smooth. By utilizing glass spheres within the wet plating processes described in the various applications above, the metal particles plate the articles and not the glass. Suitable glass spheres or spheroids are known as Ballotini (size range of about .10 mm. to 1.5 mm.) and other size ranges of glass spheres, for example, 5 mm. The inherent characteristics of unusual hardness, microscopically smooth surfaces, non-fracturability, nonplateability, and low density make such spheres ideally adapted for use as an impacting medium in the mechanical wet plating processes described.

In lieu of glass, very small spheroidal iron shot having a substantial coating of glass or vitreous enamel, or other such material is usable. The medium should be non-ionizable, smooth surfaced and substantially unreactive with water. Additionally, materials such as hard surfaced ceramics may be suitable. An important characteristic is that the film-forming material used in the wet plating process does not form a molecularly thin film on the impacting medium to attract similar films on the metal particles and produce a coating. Such materials as are not conducive to creating a surface-active effect with the film-forming material are particularly suitable, with glass being the most desirable.

The impacting medium may in some instances be hollow to reduce its density, but one of the important characteristics is that the surface of the impacting medium be very glossy, very smooth and hard and free of pores and, moreover, that this surface be regular in shape and Without any sharp radii. An important aspect of the use of the new impacting medium is that, whatever the shape thereof, there should be no tendency for the medium to lodge in the work or articles that are being coated. Moreover, the shapes of the new non-plateable impacting medium should be such as to facilitate the ready sliding and impacting of the Work, and this has actually been found to be the case in the present invention. Moreover, the utilization of a plurality of these impacting media provides for a rather highly permeable mass of the same and thus eliminates the segregation of either the Work or articles to be coated or the impacting medium itself. Stated another way, when the non-plateable impacting medium of the present invention is utilized in a ball mill, the relative movement between the impacting medium and the articles to be coated is free. The impacting sliding motion takes place and segregation of the work and/ or the impacting medium is not effected. Consequently, the metal cladding or coating of the articles is effected in a minimum of time as regards similar known mechanical metal plating processes.

The density of the impacting medium according to the present invention preferably should not be below 1.2

and should not exceed 7. The range of density will of course depend on the type of articles to be plated and the type of metal particles used for the coating. The density in effect helps to determine characteristics of the coating by determining the amount of plastic distortion of the particles on impact.

A very good coating with the present invention has been obtained by utilizing metal powders which have particles falling within the range of 3 to 40 microns, and in which a substantial portion, at least percent by weight, of the non-metallic impacting medium is in the size range of 0.10 mm. to 1.5 mm. Further, good results with regard to the non-plateable impacting medium have been obtained wherein the minimum radius of curvature of any surface projection which may be present is of the order of microns. Additionally, I have found that by using a fraction of at least 15 percent by weight of the impacting medium in the .l-1.5 mm. size range, and the remainder of the impacting medium of larger sizes selected from the size range of from 1.5 mm. to 5 mm., very effective and desirable coatings have been obtained. When operating under these conditions, and when using a small size, nonmetal plateable, impacting medium consisting of the glass spheres or equivalents, the said medium in effect operates as a means for concentrating the mechanical energy and transferring it to the metal particles to the surface of the object to be plated.

Stating this phenomenon another way, it is believed that because of the fact that very small impacting particles may be used without abrasion, smaller recesses may be reached. Moreover, because much larger low density impactors may be used without fear of coating damage, the energy of the larger impactors supplies that which the smaller ones lack. In brief, therefore, it becomes possible to gain the respective advantages of each of a greater range of impactor sizes by a mixture thereof.

The following examples are indicative of the nature of problem solved by the invention.

1) To illustrate a dry process, 435 grams of cylindrical ceramic rods of .06 inch in diameter and 1%" in length Were placed in a symmetrical steel jar, interiorly protected with a polyvinyl chloride film, in combination with 6 pounds of glass beads having a diameter of approximately .01 inch, and 70 grams of tin powder. No liquids, or film formers were added. The mill was closed and rotated for 7 hours at 7 r.p.m. and approximately 110 F. At the end of this time the rods were found to have a uniform tin coating and to have a total end to end resistance of .35 ohms. The glass beads were thinly plated with tin.

(2) The glass beads used in Example 1 were then separated and used repeatedly in other dry plating processes. As use continued, plating on the glass beads increased.

(3) To illustrate a wet plating process, 500 pounds of descaled copper-dipped steel hose clamps were placed in a hexagonal tumbling barrel along with 800 pounds of steel pellets .53 d, 7 /2 pounds zinc dust 3 to 8 micron size, three pounds of citric acid, one pound of a water soluble ethylene oxide condensed fatty acid type film-former as described in Re. 23,861, and sufficient water to cover. The barrel was rotated for one hour at 22 r.p.m., and a bright metallic coating resulted on the clamps. However, there was also a substantial coating of zinc on the steel pellets.

(4) The steel pellets from Example 3 were removed and used repeatedly in similar processes. The coatings on the pellets were found to increase continually.

The following examples are illustrative of the present invention.

(5) Mill Charge30" diameters (d) x 16" length (l) octagonal 400 lb. glass beads.015"-.037"d 200 lb. 8 nails, degreased, etched, coppered 16 lb. zinc 2 lb. polyoxyethylene substituted oleic amide 5 lb. citric acid Water to cover settled charge by 2" Operating conditions: 1% hrs., 22 r.p.m.

Results: Bright, lustrous zinc coating of .003 on the nails with no coating of the glass beads (6) Mill Chargehexagonal, 4500 cc. vol.

4 lb. .10-1.5 mm. glass spheres 6 lb. ceramic cones, .5 micron pores, .06" min. radius of curvature, D4.6

4 /2 lb. steel stampings, degreased, etched, coppered 25 g. Zn dust 10 g. citric acid 5 g. polyoxyethylene substituted oleic amide 1500 cc. H O

Operating conditions: hr., 48 r.p.m.

Results: Bright zinc coating of .0005" on the stampings with no coating of the spheres or cones (7) Mill Charge-hexagonal 4500 cc. vol.

3 lb. 8 nails, degreased, etched, coppered 6 lb. glass beads.0l5-.037 diameter 50 g. cadmium powder 5 g. polyoxyethylene substituted oleic amide 10 g. citric acid Water to cover settled charge by 1" Operating conditions: 1 hr. at 72 r.p.m.

Results: Bright, lustrous cadmium coating of .001" on the nails with no coating on the beads.

(8) Mill Charge-hexagonal 4500 cc. vol.

3 lb. 8 nails, degreased, etched, copper 6 lb. glass beads.015"-.037" diameter 10 g. aluminum alloy powder (50% aluminum, 45% tin,

5% zincweight percentage) 5 g. polyoxyethylene substituted oleic amide 10 g. citric acid Water to cover settled charge by 1" Operating conditions: hr. at 72 r.p.m.

Results: Bright, lustrous coating of .0006 on the nails without coating of the glass beads.

(9) 2 lbs. of iron clout nails were degreased in an alkaline degreasing solution, pickled in hot dilute sulphuric acid and coated with a very thin film of copper by a short immersion in a copper sulphate solution. They were then plated with zinc in a 1 gallon porcelain pot mill containing 10 lbs. of Ballotini, 750 cc. of water, 6-5 cc. of an aqueous promoter containing 16 gm. of citric acid, 4 gm. of a idisubstituted amide solubilized with ethylene oxide the remainder being water and gm. of zinc dust. The mill was rotated for 1% hours at 72 r.p.m. and a coating of 0.002" of zinc on the nails was obtained, without a coating on the Ballotini.

(10) 50 lbs. of steel spring washers were degreased as in Example 9, blasted and then given a copper coating as in Example 9. They were then plated with zinc in a rubber-lined hexagonal barrel 1 ft. x 1 ft. 4 ins. across the flats, containing 50 lbs. of Ballotini, gallon of water, 1 pint of the promoter solution used in Example 9 and 350 gms. of zinc dust. The barrel was rotated for 20 minutes at 40 r.p.m. and a coating of 0.0003" of zinc was obtained. Again, there was no coating on the Ballotini.

(11) 75 lbs. of iron chains were degreased and given a slight acid pickle as in Example 9. They were then plated with brass using the barrel described in Example 12 containing 60 lbs. of Ballotini, 1 gallon of water, 1% pints of the promoter solution used in Example 9 and 200 gms. of brass powder. The barrel was rotated for 1% hours at 40 r.p.m. and a coating of 0.0002" of brass on the chains was obtained.

(12) 112 lbs. of diamond curved washers were degreased in an alkaline degreasing solution, pickled in hot dilute sulphuric acid and coated by a very thin film of copper by a short immersion in a copper sulphate solution. They were then plated with zinc in a barrel 2' by 1'6" across the flats containing lbs. of Ballotini, 90 lbs. of

3 to mm. glass balls, 4 litres of water and 2 pints of the aqueous promoter solution used in Example 9 and 4% lbs. of zinc. The barrel was rotated for 30 mins. at 35 rpm. with 4 lbs. of crushed bauxite and 1 litre of water. was obtained.

(13) 4 lb. of small compression springs were degreased as in Example 12 and tumbled for 1 hour at 72 rpm. with 4 lbs. of crushed bauxite and 1 litre of water. This operation effected descaling of the metal. They were substantially given a thin film of copper as in Example 12. They were then plated with zinc in a 1 gallon porcelain pot mill containing 4 lbs. of Ballotini, 3 lbs. of 1.5 to 3 mm. balls and 4 lbs. of 3 to 5 mm. balls, 300 cc. of water, 30 cc. of the promoter solution as used in Example 9 and 25 gms. of zinc dust. The mill was rotated for 2 hours at 72 rpm. and a coating of 0.0006" of zinc on the springs was obtained.

In every case, the impactors were not coated. The articles mechanically coated with the unique coating of the present invention indeed were of varied kinds, sizes and shapes, both small and large. These articles, for instance, can be nuts, bolts, screws, etc., of varying sizes and other articles irregularly shaped and having right angular formations and having corners, both interior and exterior, and all sorts and sizes of many other articles which are susceptible to a mechanical metal plating.

Effective coatings were obtained using metal particles or flakes of zinc, tin, lead, cadmium, copper, brass, aluminum, etc. and alloys thereof.

It will be seen from the hereinbefore set forth examples and description of the invention that a new mechanical metal plating process, a new mechanically formed metal coating, a new non-metal plating preferably non-metallic impacting medium and finally a new metal coated article are disclosed.

What I claim is:

1. In a method of metal plating the surfaces of articles with metal, the steps comprising: mixing in a container a quantity of metal articles to be plated in a liquid carrier with a quantity of particles of a selected metal powder, the liquid carrier being suiiicient to cover the articles and particles; adding a substantial quantity of impactor material consisting of hard bodies having entirely microscopically smooth non-metallic and non-ionizable outer surfaces resistant to metal coating in the liquid carrier; agitating the container to forceably impact the particles on the articles by the bodies to form a coating layer of particles on the surfaces of the articles; and continuing the agitation to build up the coating to a desired thickness by increasing the number of particles permanently adhering to the articles and to other adhering particles.

2. In a method of mechanically wet plating the surfaces of metal articles with metal comprising the steps of mixing in a container a quantity of metal articles to be plated, particles of a selected metal powder, and a liquid carrier sufiicient to substantially cover the articles and particles and promote adhering of the particles to the surfaces of the articles; the improvement comprising the adding of a substantial quantity of impactor material consisting of hard bodies having completely microscopically smooth non-metallic and non-ionizable outer surfaces resistant to metal coating in the liquid carrier and then agitating the container to forceably impact the particles onto the articles to form a coating of layers of particles perm-anently adhering to the sunrfaces of the articles, without any coating of the particles on the impactor material.

3. In a method of mechanically wet plating surfaces of metal articles with metal, the steps comprising: mixing in a container a quantity of metal articles to be plated in a liquid carrier with a quantity of particles of a selected metal powder, the liquid carrier being sufficient to substantially cover the articles and particles and including a surface-active compound dispersable into a molecularly t-hin film on the surfaces of the articles and the particles: adding a substantial quantity of impactor material consisting of hard impactor bodies having entirely microscopically smooth non-metallic and non-ionizable outer surfaces resistant to metal coating and nonattractive to the formation of films of the surface-active compound thereon; agitating the container to forceably impact the particles onto the articles by the bodies to form a coating layer of particles on the surfaces of the articles, and continuing the agitation to build up the coating on the article surfaces by multi-layers of adhering particles without coating the impactor bodies with particles.

4. In a method of mechanically wet plating the surfaces of metal articles with metal, the steps comprising mixing in a container a quantity of metal base articles to be plated in a liquid carrier with a predetermined quantity of particles of a selected metal powder, the liquid carrier including a substantial amount of Water and a surfaceactive film forming compound unreactive with the water and dispersable to form a highly attractive molecularly thin film covering the surfaces of the articles and the particles; adding a substantial quantity of impactor material consisting of hard impactor bodies of entirely microscopically smooth non-metallic and non-ionizable outer surfaces resistant to the formation of films of the compound thereon and unreactive with water; agitating the container to forceably impact the particles on the articles by the bodies to form a coating layer of particles permanently adhering to the surfaces of the articles, and then continuing the agitation to build up the coating to the desired thickness by increasing the build up of layers of particles onto the articles without coating of the impactor material with particles.

5. In the method of mechanically wet plating the surfaces of metal articles with metal, the steps comprising:

(a) mixing in a container (1) a quantity of metal articles to be plated,

(2) a predetermined quantity of particles of a selected metal powder suflicient to coat the surfaces of the articles to a desired depth,

(3) a carrier liquid including an organic surfaceactive compound dispersed in water, the surfaceactive compound being exhaustible to form a strongly adherent, molecularly thin film on the surfaces of the articles and the metal particles to aid in attracting the particles to the articles, and

(4) a substantial quantity of impactor material consisting of hard spheroidal bodies having entirely microscopically smooth non-metallic outer surfaces nonreactive to water and resistant to the formation of films of the compound thereon, the carrier being sufficient in amount to substantially cover the articles, particles and the impactor material; and

(b) then agitating the container sufiiciently to forceably impact the particles onto the articles by the bodies to form a coating of permanently adhering particles on the article surfaces to the desired depth Without coating the impactor material with the particles.

6. The method according to claim 5 wherein the carrier includes a fluxing compound reactive to oxides of the selected metal to remove the oxides and enable the surface-active compound to form a film on clean metal, and

the bodies of impactor material are nonreactive with the fluxing compound.

7. In the method of mechanically wet plating the surfaces of metal articles with metal, the steps comprising:

(a) mixing in a container (1) a quantity of metal articles to be plated,

(2 a predetermined quantity of particles of a selected metal powder sufiicient to coat the surfaces of the articles to a desired depth,

(3) a carrier liquid including an organic surfaceactive compound dispersed in water, the surfaceuctive compound being exhaustible to form a strongly adherent, moiecularly thin film on the surfaces of the articles and the metal particles to aid in attracting the particles to the articles, and

(4) a substantial quantity of impactor material consisting of hard spheroidal bodies having entirely microscopically smooth outer surfaces of non-ionizable glass resistant to the formation of films of the surface-active compound thereon, the carrier being sufiicient in quantity to substantially cover the articles, particles and the glass surfaced bodies of impactor material; and

(b) then agitating the container sufficiently to forceably impact the particles onto the articles by the bodies to form a coating of permanently adhering particles on the article surfaces to the desired depth without coating the impactor material with the particles.

8. The method according to claim 7 wherein the bodies of impactor material are made entirely of glass and the impactor material consists of at least 15% by weight of bodies having a size in the nange of .1 to 1.5 mm. and the remainder of the bodies being in the size range of 1.5 to 5 9. The method according to claim 8 wherein the carrier includes a fiuxing compound reactive to oxides of the selected metal to remove the oxides and enable the surface-active compound to form a film on clean metal, and the bodies of impactor material are nonreactive with the fiuxing compound.

10. The method according to claim 7 wherein the surface-active compound is a substituted amide solubilized with an ethylene oxide.

11. The method according to claim 10 wherein the carrier includes a fiuxing compound of citric acid reactive with oxides of the selected metal to remove oxides from the particles and enable the surface-active compound to form a film on clean metal surfaces of the particles.

12. The method according to claim 7 wherein the selected metal consists of at least one selected from the group consisting of zinc, cadmium, tin, aluminum, copper, lead, and alloys thereof.

References Cited UNITED STATES PATENTS Re. 23,861 8/1954 Clayton l17109 2,689,808 9/1954 Clayton 117-109 X 2,788,297 4/1957 Louis 117-1 09 X 2,817,604 12/1957 Louis ll7l09 X 3,023,127 2/1962 Clayton 117109 3,164,448 1/1965 Pottberg 117-109 X 3,132,043 5/ 1964 Clayton 117-109 ALFRED L. LEAVITT, Primary Examiner.

J. R. BATTEN, JR., Assistant Examiner.

US. Cl. X.R.

ll7l31 

